The standard p-zombie argument usually goes something like this:
- If physicalism is true, then p-zombies are metaphysically impossible.
- If something is conceivable, then it is metaphysically possible.
- P-zombies are conceivable.
- Therefore, p-zombies are metaphysically possible. (from 2,3)
- Therefore, physicalism is false. (from 1,4)
It would be best to first define some terms. By physicalism, we mean identity physicalism, which we define as the belief that mental states are identical to physical states. If we adopt Kripke’s notion of rigid designators, that is, terms that refer to the same objects in all possible worlds, we have that mental events are identical to physical events in all possible worlds. By metaphysical possibility we mean nothing more than logical possibility, i.e., truth in at least one world accessible by the actual one. Finally, a p-zombie is a hypothetical entity that is physically identical to a human, yet does not have any qualitative experience (“qualia”).
We now walk through the argument. Premise 1 is true for the following reason: if there exists a possible world in which p-zombies exist, then there exists a possible world in which mental events are not identical to physical events, since the p-zombie is physically identical to a human but has no qualia. Premises 2 & 3 are the most controversial premises of the argument. We discuss them each in turn.
Premise 2
I believe that this premise is true almost by definition. An intuitive justification for the premise is that, if there were a conception that was metaphysically impossible, then there would be a contradiction involved in the conception, which is absurd. It does not make much sense to say that one can conceive of, say, a round square. It does make sense, however, to mistake an attempted conception of a round square as a conception of a round square. So it seems the entire argument hinges on whether we can indeed conceive of p-zombies.